Fiber Products
Description
Dietary fiber is a group of plant polysaccharides which resists digestion in the gastrointestinal tract. They remain in the ileum, partially hydrolyzed by bacteria in the colon.
Dietary fiber is not a single plant substance, but an extremely complex variety of substances, including: cellulose, hemicellulose, pectic substances, gums, mucilages, algal polysaccharides (e.g. agar and carrageenan) and lignin, a non-polysaccharide.
These groups of fibers can be further divided into the soluble and insoluble dietary fiber groups. Soluble fibers include gums, pectins, mucilages and some hemicelluloses. Insoluble fibers include cellulose, lignin and some hemicelluloses. Most foods of plant origin supply both the soluble and insoluble forms of dietary fiber.
Generally, vegetables and grain products are good sources of cellulose, while other whole-grain cereals and bran products are more concentrated sources of hemicellulose. Oat products and legumes are good sources of gums. Most citrus fruits and apples provide ample amounts of pectin.
Interest in recent years about the role of dietary fiber has increased with the knowledge such fibers are useful in the prevention and treatment of constipation and possibly other chronic diseases, such as non-insulin-dependent diabetes mellitus.
The 1988 U.S. Surgeon General Report on Nutrition and Health recommends increased consumption of whole grain foods and cereals, as well as vegetables (including beans and peas), and fruits. A similar recommendation was released three years earlier in 1985 by the U.S. Department of Agriculture in Nutrition and Your Health: Dietary Guidelines for Americans, 2nd Edition.
In recent years additional areas of potential therapeutic benefits have been studied, including: weight management; colon cancer; diverticular disease; control of blood lipids (fats); and, non-insulin-dependent diabetes and other disorders of carbohydrate metabolism.
Most polysaccharides can be grouped as follows:
| Pectic substances | Arabinans | |
| Galacturonans | ||
| Galactans | ||
| Arabinogalactans | ||
| Hemicellulose | Mannans | Glucomannans |
| Galactomannans | ||
| Galactoglucomannans | ||
| Xylans | Arabinoxylans | |
| Glucuronoxylans | ||
| Cellulose | Glucans | Beta-glucans |
| Others | Xyloglucans (amyloid) |
Each polysaccharide possesses different properties making it preferable over the rest as a dietary fiber supplement. For example, glucomannan has stronger gel-forming properties than either pectin or guar gum. Additionally, unlike other gel-forming dietary fibers such as pectin, glucomannan is tasteless and does not adhere to the palate when eaten.
See also
Fiber - Natural
High Fiber Diet
Low Fiber Diet
Method of Action
Gel-forming fibers interfere with the motility and absorption of nutrients from the gut. When these fibers are consumed, gels are formed around the food particles increasing the viscosity of the stomach contents and creating a sensation of "being full".
The gels interfere with the action of digestive enzymes and thus slow the rate at which sugar and fat enters the blood stream, eventually increasing the amount of fecal bulk passing through the large intestine.
Therapeutic Approaches
In general, the reported physiological effects of dietary fiber are gastro-intestinal:
1. Binding of bile acids
2. Lowering of blood cholesterol
3. Increased satiety after eating
4. Increased fecal weight and volume
5. Decreased transit time of food through the colon
6. Decreased insulin response after a carbohydrate meal
A consensus exists that most people can derive a substantial amount of dietary fiber by regularly eating a wide assortment of nuts, legumes, whole-grain cereals, breads, fruits and vegetables. Animal meats and organs, however, are very poor sources of soluble and insoluble fiber.
Oat bran and barley are rich sources of water soluble fibers, glucans and beta-glucans. Like fruits and vegetables, these two cereal grains decrease blood cholesterol levels and reduce the rate of stomach emptying. The clinical aspects of the various fibers can be divided as follows:
A serving of high fiber food can yield as much as 5 gms of fiber. A high fiber diet is considered to be above 20 gms (4 servings).
Gums, mucilages and pectins
Because of their viscosity, these dietary fibers decrease gastric emptying and retard absorption of the food from the small intestine. Clinically, these fibers have potential in the treatment of non-insulin-dependent diabetes, carbohydrate metabolic disorders, hypercholesterolemia, and the dumping syndrome.
Polysaccharide-lignin mixtures, pentosanes and wheat bran
Because of their particle size and water-holding capacity, these dietary fibers increase gastric motility, decrease intestinal transit time, decrease pressure in the lumen of the colon and increase fecal bulk. Clinically, these properties could have potential in the treatment or prevention of constipation, diverticular disease and peptic ulcers.
Acidic polysaccharides, such as pectins
These dietary fibers cause a reduction in the amount of heavy metals absorbed from the small intestine.
Lignin
This dietary fiber has antioxidative (free radical scavenging) properties, decreasing the numbers of free radicals found in the small intestines. Clinically, this fiber could reduce the absorption of carcinogens from the intestinal tract.
Lignins and pectin-mixed fibers
Because of their adsorptive properties, these dietary fibers increase the output of steroids in the feces, while also increasing fecal fat and nitrogen losses. Clinically, this has potential in the treatment of hypercholesterolemia and cholelithiasis.
Polysaccharides (free of ligni)
These dietary fibers increase flatulence and lower the pH of the feces, due to their effect on colonic bacteria. This action offers no particular therapeutic benefit, other than perhaps lessening or preventing constipation.
Strong support exists for fiber's role in the treatment of non-insulin-dependent diabetes mellitus constipation and diverticulitis.
Weight management of obesity
Although a high fiber diet has been promoted for weight loss, controlled, long-term trials have not established this to be true. Transient weight loss from a high fiber diet may not provide long-term results. At this time the data remains contradictory. However, in a program of education and diet management, increased fiber intake may be beneficial if considered a part of a balanced diet. Other factors, such as energy expenditure, frequency of eating, etc., deserve equal consideration in weight management strategies.
To date, heredity, overeating, and physical activity remain important factors in the causation of obesity. Nevertheless, the rationale for using high-fiber supplements is understandable: obesity is rare in populations on a high fiber diet, and more common in populations consuming a low fiber diet; fiber-deficient foods are less satiating than fiber-rich foods; fiber-deficient foods are calorically more concentrated than unprocessed foods; and increased fiber contain promotes longer chewing time, which retards the rate of food ingestion.
Toxicity Factors
Excessive intake of dietary fibers can produce reversible side-effects, including intestinal distention (bloating), flatulence (gas), or diarrhea. A few cases of colon and esophageal obstruction have been reported. The former from inappropriately consuming too much dried powdered glucommanan, and the latter from the abuse of supplements and laxatives containing soluble and insoluble fiber.
Too often people are not being advised to increase their consumption of liquids, particularly water, to avoid esophageal or colonic obstruction. To date there are no reports of gastrointestinal obstructions from fiber ingested with adequate amounts of water.
References
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